This invention relates to air assist fuel injection systems and more particularly to throttle control of the compressor air intake in such systems.
It is known in the art to provide direct injection of fuel to the cylinders of an internal combustion engine using air-assisted fuel injection wherein compressed air is provided to assist in the injection of fuel into the cylinders. A compressor for providing compressed air for such a system may be directly driven by the engine so that the compressor speed varies directly with that of the engine. However, the output flow of the engine-driven compressor is not linear with the engine speed related requirement for proper fuel delivery. Accordingly, the air compressor displacement is sized for the greatest flow demand in the engine speed/load matrix plus a factor for expected deterioration of the system over time.
Because of this over capacity, an air pressure regulator is utilized to control the system pressure at a nominal pressure level and to exhaust excess air flow supplied by the compressor. The result is that the compressor operates most of the time with considerable excess air flow which is parasitic in that it consumes excess energy in pumping air not needed for operation of the engine. Accordingly, an improved system for reducing the parasitic losses caused by excess air flow of the compressor with a minimum of additional cost is desired.
The present invention provides an improved air-assisted fuel injection system wherein the compressor air inlet includes an inlet flow regulating device, such as a throttle, wherein the throttle is controlled in response to the exhaust air flow from the air pressure regulator. The system operates to provide a low nominal exhaust air flow from the air pressure regulator by controlling the throttle position in the intake of the air compressor. An air flow indicator associated with the air pressure regulator connects through a feedback system with a controller for variably closing or opening the throttle in response to increasing or decreasing excess air flow from the pressure regulator.
If the air pressure regulator exhaust flow is too high, the feedback system and controller operate to restrict the input air flow to the compressor by moving the throttle in a closing direction. If the regulator exhaust flow is too low, the feedback system operates with the controller to open the throttle and increase air flow to the compressor. In this way, equilibrium at a prescribed low nominal regulator exhaust flow is reached quickly, within a few compressor cycles.
Various forms of air flow sensors or indicators could be used. Some examples are an air flow meter measuring exhaust flow from the pressure regulator and a position transducer measuring movement of a pressure responsive diaphragm valve or other member in the pressure regulator.
These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings.